1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an apparatus for detecting the presence of a developing unit assembly formed by a plurality of developing units and an image forming apparatus employing the same.
2. Description of the Related Art
An electrophotographic image forming apparatus, such as a laser printer, a light emitting diode (LED) printer, a facsimile, a digital photocopier, or a multifunction device, generates visible images on a printing medium in response to digital signals input from a computer or a scanner by performing a series of image forming processes.
In a typical image forming apparatus, a developing unit assembly is an integral structure so that the entire developing unit assembly can be exchanged as necessary. There are various reasons for exchanging a developing unit, including removing and replacing the developing unit when inner parts of a main body of the image forming apparatus must be cleaned or repaired; replacing the unit when the photosensitive medium reaches the limit of its useful lifespan, and replacing the unit when the developer in the unit is exhausted. Integral developing unit assemblies are generally one of two types. In the first type, a photosensitive medium, a developing roller and a developer container are all integrated into one, single developing unit. In the second type, the developer container and the developing roller are formed into one unit and the photosensitive medium is formed as another unit. These two units together make up the developing unit assembly.
FIG. 1 is a cross-sectional view of a conventional image forming apparatus with the second type of developing unit assembly, that is, a developing unit assembly formed by two units. The developing unit assembly 150 of the image forming apparatus is mounted inside a mounting portion 120 of a main body 110. The developing unit assembly 150 includes a first developing unit 160 and a second developing unit 170. The first developing unit 160 includes a developer container 164 and a developing roller 162, and the second developing unit 170 includes a photosensitive medium 172. In a large capacity image forming apparatus, the second developing unit 170 typically has a lifespan three to four times longer than that of the first developing unit 160. Hence, the first developing unit 160 is exchanged more frequently than the second developing unit 170.
The first and second developing units 160 and 170 are mounted on the mounting portion 120 so that they function integrally during operation of the image forming apparatus. In other words, although not illustrated, a charging roller charges a surface of the photosensitive medium 172 uniformly, and an electrostatic image is formed by a scanned light generated by a laser scanning unit (not shown). A developer supplied from the developer container 164 is applied to the electrostatic image to form a visible image. The visible image is then transferred onto a printing medium (which is provided from a printing paper feed unit 180) by a transfer roller (not shown). The transferred image is fixed onto the printing medium by a fixing unit and is delivered to a stacker.
A first contacting portion 166 and a second contacting portion 174 are formed on the rear sides of the first developing unit 160 and the second developing unit 170, respectively. The first and second contacting portions 166 and 174 indicate whether or not the first and second developing units 160 and 170 are installed in the mounting portion 120. A first sensing portion 116 and a second sensing portion 114 are mounted inside the mounting portion 120 of the main body 110. The first and second sensing portions 116 and 114 are located at regions corresponding to the first and second contacting portions 166 and 174 so that they contact the first and second contacting portions 166 and 174 when the developing units are installed. Preferably, the first and second contacting portions 166 and 174 include a CRUM (Customer Replaceable Unit Monitor) in the form of semiconductor chip. The CRUM stores information regarding the characteristics and lifespan of elements such as the photosensitive medium, the developing roller, and the developer.
When the first developing unit 160 and the second developing unit 170 are mounted in the mounting portion 120 of the main body 110, the first and second contacting portions 166 and 174 contact the first and second sensing portions 116 and 114, respectively. Therefore, the image forming apparatus detects the presence of the developing unit assembly 150, as well as any information stored by the CRUM which is required for printing operations.
In the conventional image forming apparatus described thus far, the first and second contacting portions 166 and 174 are formed in the first and second developing units 160 and 170, respectively. Thus, the first and second sensing portions 116 and 114 must be installed at corresponding regions of the main body 110. However, a driving unit 117 for driving the developing roller 162 and the photosensitive medium 172, and a power transfer unit 118 for transferring power from the driving unit 117 to the developing roller 162 and the photosensitive medium 172, must also be installed in the main body. Since all of these parts must be installed in the same general area, it is difficult and complicated to find suitable mounting locations for the multiple contacting portions 166 and 174 and sensing portions 116 and 114. Thus, the use of a plurality of contacting and sensing parts increases the required size of the image forming apparatus as well as its manufacturing cost, and hinders the development of a smaller, more cost-effective image forming apparatus.
Accordingly, there is a need for an image-forming apparatus with an improved apparatus for detecting the presence of a developer unit formed of a plurality of parts.